A silicon carbide (SiC) semiconductor has a wide band gap that is wider than that of a silicon (Si) semiconductor, and in comparison with a Si semiconductor device using a Si semiconductor, a SiC semiconductor device using a SiC semiconductor is excellent in breakdown voltage property, having a high allowable current density, and is high in heat resistance, therefore, an operation under a high temperature can be performed.
For example, in Metal Oxide Semiconductor Field Effect Transistor (MOSFET) using SiC, the gate insulating film that is an upper Junction Field Effect Transistor (JFET) region and, to which a high electric field is easily applied structurally, an electric field strength to be applied to the gate insulating film is maintained low, thereby suppressing destruction of the gate insulating film when a high voltage is applied.
For example, in a semiconductor device disclosed in Patent Document 1, a P− region in which a p-type impurity concentration is relatively low is provided in a JFET region of the SiC-MOSFET, thereby, in comparison with the structure without the P− region, suppressing the electric field strength applied to the gate insulating film that is the upper JFET region, therefore, credibility thereof when the high voltage is applied to the device is improved.
Also, a technique is developed, in which, in a semiconductor device, semiconductors each having a different band gap from one another are brought into ohmic contact in part with each other, thereby reducing an on-resistance. In patent Document 2, a technique in which the impurity concentration is set to high at a portion to be ohmically connected in heterojunction of semiconductors, thereby reducing the on-resistance of the whole device.